Study On Cracking Mechanism And Control Measures Of The Secondary Lining Of Linpanshan Tunnel

Lining cracking leads to tunnel leakage,reinforcement corrosion and tunnel disease,which has a serious i MPact on tunnel construction and operation.Therefore,it is of great engineering application value to study the causes of tunnel secondary lining cracking and put forward targeted treatment measures.Based on the construction of Linpanshan Tunnel High-speed Railway,this paper conducts an on-site investigation and analysis of the lining cracking phenomenon in the Class II surrounding rock section of the tunnel construction,and makes a preliminary analysis of the reasons for the lining cracking;Using numerical simulation analysis method,the stress characteristics of tunnel lining under the conditions of different Angle inclined strata and different thickness strata are simulated.Based on the analysis of numerical simulation results,the causes of cracking of hard layered sedimentary rock lining are found out,and the engineering countermeasures to prevent the excavation of lining are suggested.The deformation of surrounding rock and the stress of lining were monitored closely following the progress of tunnel construction,and the results of numerical simulation were verified.The research results are as follows:(1)The secondary lining cracking of tuff class II surrounding rock section of Linpanshan tunnel was investigated.This paper analyzes the crack location,crack width,crack depth and crack length,and puts forward the causes of tunnel lining cracking,that is,the lining cracking is caused by the uneven settlement at the bottom of the tunnel and the discontinuous deformation of the inclined layered joints of sedimentary rock.(2)Numerical simulation method is used to analyze the influence of rock inclination angle and rock thickness on tunnel lining stress and surrounding rock deformation characteristics.The results show that when the dip angle of rock is 55 ° and the thickness of jointed rock is 0.3m,the deformation of surrounding rock and the stress difference of lining on both sides of tunnel are the largest.(3)Based on the numerical simulation results,the causes of lining cracking of Linpanshan tunnel are analyzed and verified,and the corresponding engineering countermeasures are put forward,The lining structure with inverted arch and bolt support are used to eliminate the uneven settlement at the bottom of tunnel and the deformation difference of surrounding rock on both sides.On this basis,the invert depth and anchor length are optimized.(4)The deformation of surrounding rock and the stress of supporting structure during tunnel construction are monitored on site.Based on the monitoring results,the variation laws of deformation of surrounding rock,internal stress of lining,axial force of steel arch,pore water pressure and layered settlement of arch bottom with time are analyzed;At the same time,the deformation of surrounding rock and the stress of lining obtained from field monitoring are basically consistent with the numerical simulation results,which verifies the reliability of the investigation results and numerical simulation results.